How to scale multiple faces without moving them towards each other?
Set the pivot point to individual origins.
You find that on the bottom bar, the 2nd one on right of the mode selection.



(Turned this into an answer from a comment by lemon, with explicit permission.)

Note:
In order to turn the cube in the picture into something similar to the hand in yours, use "Extrude individual" on the two selected faces (or your fingers).
Then scaling them by individual pivot point has the effect I think you want to achieve.